1. Field of the Invention
The present invention relates to the growth of planar non-polar {1-100} and semi-polar {11-22} gallium nitride (GaN) with hydride vapor phase epitaxy (HVPE).
2. Prior Art
Gallium nitride (GaN) and its related compounds are prime candidates for fabrication of advanced visible and ultraviolet high-power and high-performance optoelectronic devices and electronic devices. These devices are typically grown epitaxially by growth techniques including molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), or hydride vapor phase epitaxy (HVPE).
The selection of substrate is critical for achieving the desired GaN growth orientation. Some of the most widely used substrates for III-N growth include SiC, Al2O3, and LiAlO2. Various crystallographic orientations of these substrates are commercially available.
FIGS. 1(a) and 1(b) are schematics of crystallographic directions and planes of interest in crystal cell of hexagonal wurtzite GaN. Specifically, these schematics show the different crystallographic growth directions and also the planes of interest in the hexagonal wurtzite GaN structure, wherein FIG. 1(a) shows the crystallographic directions a1, a2, a3, c, <10-10> and <11-20>, and FIG. 1(b) shows planes a (11-20), m (10-10) and r (10-12). The fill patterns of FIG. 1(b) are intended to illustrate the planes of interest, but do not represent the materials of the structure.
It is relatively easy to grow planar c-plane GaN due to its large growth stability window. Therefore, nearly all GaN-based devices are grown parallel to the polar c-plane. However, as a result of c-plane growth, each material layer suffers from separation of electrons and holes to opposite faces of the layers due to spontaneous polarization. Furthermore, strain at the interfaces between adjacent layers gives rise to piezoelectric polarization, causing further charge separation.
FIGS. 2(a) and 2(b), which are schematics of band bending and electron hole separation in a quantum well sandwiched between to barriers as a result of polarization, show this effect, wherein FIG. 2(a) is a graph of energy (eV) vs. depth (um) and represents a c-plane quantum well, while FIG. 2(b) is a graph of energy (eV) vs. depth (um) and represents a non-polar quantum well.
Such polarization effects decrease the likelihood of electrons and holes recombining, causing the final device to perform poorly. One possible approach for minimizing or eliminating piezoelectric polarization effects in GaN optoelectronic devices is to grow the devices on semi-polar planes of the crystal such as [11-22] plane or non-polar planes of the crystal such as a-{11-20} and m-{1-100} planes family of GaN. Such planes contain equal numbers of Ga and N atoms and are charge-neutral.
Planar {1-100} m-plane GaN growth has been developed by HVPE and MBE methods but only successfully on m-plane GaN substrates. However, prior to the invention described herein, planar semi-polar and non-polar GaN growth on sapphire had not been accomplished with HVPE.